Hippeastrum Diseases

Amaryllis flowers are available in different combinations of colors.

Hippeastrum, commonly known as amaryllis, is prized primarily for its large, trumpet-shaped flowers that appear in spring in clusters of two to six atop a tall flower stalk. This plant grows as a herbaceous perennial within U.S. Department of Agriculture plant hardiness zones 8 through 10, although it is cultivated as a potted plant across a much broader range. A handful of diseases can potentially prove problematic on amaryllis plants.

Red Blotch

Red blotch, sometimes also known as leaf scorch, is caused by the fungus Stagonospora curtisii. This fungal disease appears on the amaryllis leaves and flower stalks as red spots that enlarge, elongate and become sunken. Infected leaves and flower stalks generally bend at the point of infection, and heavily-infected flower stalks may break or wither before flowers can emerge. The red blotch fungus is carried on bulbs, which can then infect emerging foliage and flower stalks. While any damage to the bulb tissue causes redness, spots that indicate red blotch tend to have definite margins and outlines. Promptly destroying infected bulbs and plants, using only sterilized soil, providing the amaryllis with proper growing conditions and soaking bulbs in water kept between 104 and 114 degrees Fahrenheit for 30 minutes will help to minimize problems with red blotch.

Mosaic Virus

Amaryllis infected with the mosaic virus have a light yellow streaking on leaves that turns more yellow over time. New leaves may not exhibit the yellow streaking until they have matured. An infected amaryllis will experience reduced growth as it ages, and flowering will eventually cease. There is no way to treat an infected amaryllis plant, and it should be discarded promptly if other desirable vegetation is growing nearby to prevent disease transmission.

Botrytis Blight

Botrytis blight, also known as gray mold, is caused by the fungal pathogen Botrytis cinerea and is most problematic when conditions are cool and damp. It can cause spotting and discoloration of flowers and buds and wilt and decay of leaves. Infected portions of the plant are eventually covered by characteristic grayish-brown spore masses. Good sanitation and care practices like promptly removing spent flowers, old leaves and infected portions of the amaryllis, spacing plants well to ensure good circulation and avoiding overhead watering will prevent or address botrytis blight on amaryllis.

Bulb and Root Rots

Amaryllis bulbs are large and fleshy, making them particularly prone to rot, which is potentially caused by a variety of different soilborne fungal and bacterial pathogens. Excessive watering, poor drainage or bruising can encourage bulb rot. A diseased bulb is generally discolored and mushy, and it may smell bad. Any leaves that do emerge are yellowish and stunted. Infected bulbs and the surrounding soil are discarded to prevent spread and drainage or irrigation practices are corrected, if needed.